On my UE40MU6400 the Optical Audio Output is fixed level. You can only control the volume of the TV's speakers (or mute them altogether) from the TV remote. This arrangement quite suits me as I have the Optical Output running to a HiFi system which I might use when viewing a Music Program but not in everyday use. I can use the HiFi system's remote control to adjust the HiFi volume independently of the TV speakers. I'm pretty sure all the Samsung TVs work like this.
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